Hi @Doria
Have a look at this article which explains how to configure the certificate for AD to use. https://learn.microsoft.com/en-us/troubleshoot/windows-server/identity/enable-ldap-over-ssl-3rd-certification-authority
Also have a read of this post, as setting up LDAPS doesn't mean applications will automatically use an LDAPS connection. https://learn.microsoft.com/en-us/answers/questions/558210/lad-over-ssl.html
And once you have setup the certificate you can use this article to confirm that the certificate is installed and working correctly. https://nettools.net/howto-troubleshoot-ad-ldaps-connection-issues/
Gary.